Optimum settings for hot water/heating timer

howisthisriskfree

I was hoping you may help settle a discussion between me and the OH about the settings for the programmable timer. We moved a few months back from a really old place to a really new one so things are still unfamiliar, especially the heating (don't think we have put it on yet because the temperature has not got low enough)

Here is what we are working with:

Hot water: Large 'megaflo' unvented tank. Heated via electric (no gas in property).
Heating: Underfloor heating controlled by thermostat in each room (set to 22), I assume this is overridden by the 'CH' setting on the timer.. There is no 'fall back' temperature setting as far as I can see.
Schedule: 2 people in the house, a shower in the morning (ie 7-8am) and bath-time in the evening on weekdays.

At the moment both CH and HW are timed to come on for 2 hours in the morning and 4 hours in the evening (this reflects our old house setup) but for hot water I sense this must be really inefficient, as the tank is large and being modern will probably keep the water hot for ages.

But then for the underfloor heating, I am not sure that this is the best way to run it and it should go all the time, although I get concerned with the cost of running the thing all the time, and also if the two different settings are on at different times, the CH 'robbing' hot water that means the shower/bath becomes cold!

What would be the most efficient settings for me to program into the timer?

getmore4less

the CH 'robbing' hot water that means the shower/bath becomes cold!

What do you mean by this? is the underfloor wet and also heats the water or just electric mats and immersion in the tank .

Underfloor heating controlled by thermostat in each room (set to 22),

I would aim for 19c-20c.

one issue potentially with underfloor is the hysteresis is quite long so if you let the rooms go cold you per heat time will be longer
ie to be up to temp at the time you want you need to start heating well before.

you can test the hot water tank losses by heating it up and then leaving it for 24hr and see how much is loses.

if it is a big tank does it have top and bottom heaters?
For 2 people you may find just heating the top is enough for the morning showers

howisthisriskfree

Hi

Yes, the underfloor heating is run by hot water as well. The manifold distributes the water to the coils and also towel rails.

You are correct, it seems to take ages to come on, if at all. And with the thermostat at 22, the floor is not noticeably warm though, although according to the thermometer the rooms are already at 22. The towel rails in the bathroom heat up fast enough though.

No idea if the tank has top and bottom heaters, but I am sure it lasts at least 6 hours so far, just wondered if the hot water setting was off but the central heating was on, all the water in the tank would be used for the coils.

Heedtheadvice

You are wise to think of how to control it best as electricity can be very expensive (but very efficient) costing lots more than gas. Setting things to use minimum energy consistent with need and convenience should be your aim finance wise.

Room settings are a little high, 20 or 21 should be adequate for most but the infirm, very young or elderly. You get good even heat with your method but no radiant heat to speak of and radiant heat feels nice! Perhaps you miss that a bit! The floor heating takes a long time to heat up because of the thermal inertia but will maintain it for a fairly long time (unless in a drafty environment such as a poor house or lots of ventilation). Set the control for Ch to come on a few hours before need in the morning. It can go off then before hot water heating is required.

Ensure your tank thermostat is not set too high 60 degrees Celsius should be max but towards the lower figure of 50 might be acceptable if you have a big tank fully heated? You will need to experiment with what you are happy with. Set you hot water to heat at the end of the Ch time in the morning (or towards the end of you can have changed and he heating on together.) Working backwards and depending on how long hot water and Ch take to heat up you can then work out times. For example if it takes an hour for water to heat and four for Ch to come to temp in rooms and you want to use at 7a.m. water from 6 to 7 and Ch from 2 to 6. Hopefully you will not need nearly as long as that especially not mid winter!
You might get away with much less, especially if you go out to work at say 8a.m. as all the stored heat will be partially wasted during the day.

Similar timing for the evening depending upon how well heat is stored as posted above.

I have gas powered underfloor heating in part of our house rads on the rest. The underfloor heating is only on during the colder parts of the year and just tops up every night/morning but is set quite low. Fine for a working rather than sitting area until we leave doors or windows open too long!

You might review you room by room temp settings. We like coolish bedrooms, warm bathrooms and lounge. They need not all be set the same but there might be some interaction if doors are not closed!

Trial and error might be you best way of finding out what is best for you but if you let your house get too cold it will take longer to heat up! A radiant fire in your living area might be good?

getmore4less

Indirect water heating seems redundant and inefficient if using electric immersion would be better.
Might make more sense with solar.

Do you have op peak rates?

Apodemus

Heedtheadvice wrote: »

Ensure your tank thermostat is not set too high 60 degrees Celsius should be max but towards the lower figure of 50 might be acceptable if you have a big tank fully heated?

Good advice, but always a difficult balance between efficiency, scald risk, and Legionella prevention.

getmore4less

Apodemus wrote: »

Good advice, but always a difficult balance between efficiency, scald risk, and Legionella prevention.

I have a temp/time water system, set to shower temp for one period with a hotter cycle for bath time when needed.

If we use more or have people it gets modified to be on longer and hotter.

nofoollikeold

Are you sure your hot water cylinder is unvented? or is it a thermal store. If electrically heated it will be a direct type, where the water inside is heated by direct contact with the immersion heater(s). If this same water was used to supply underfloor heating, the water you wash in would have been circulated through the underfloor heating pipes.

A thermal store maintains a large volume of hot water, which can also be used for heating (underfloor or radiators) and domestic hot water is obtained by passing incoming cold mains water through a heat exchanger, the hot side of which is the water from the store.

If its a thermal store, the water in the cylinder will need to be kept high (80 degrees or thereabouts) to heat domestic hot water as its drawn off. The key to efficiency is usually making sure the bottom immersion heater is connected to a low tariff supply (e.g. Economy 7) so that the whole cylinder heats up overnight.

Heedtheadvice

Some more very good pointers there, especially by Apodemus regarding legionella. If you do turn to cooler hot water, every month or so turn it up higher for a cycle as that will kill off the any bacteria that might have started multiplying!
Minimum value for hot water storage ought to be 50 and the hotter cycle above 60, say 65 with enough time for the whole cylinder to get hot, then back to your preferred temperature.